1. Field of the Invention
The invention in general relates to microwave signal processing, and particularly to an improved input or output for a magnetostatic wave device.
2. Description of the Prior Art
In the field of microwave signal processing, use is made of a device which provides a predetermined delay or predetermined filtering action to the microwave signals. Such devices find multiple uses in such areas as signal correlation, communications path length equalizer, electronic counter measures, frequency synthesis, Fourier transformation, and oscillators, to name a few.
A popular device of compact construction which performs signal processing is the surface acoustic wave (SAW) device which basically includes a plurality of interdigital transducer fingers positioned on a substrate such as a piezoelectric material. A signal applied to the interdigitated fingers is launched as a surface acoustic wave in the piezoelectric which includes a similar interdigitated electrode array spaced from the launching array to reconvert the acoustic wave back to a microwave signal. SAW devices are extremely useful in the microwave region up to about 2 to 3 gigahertz (GHz). At higher frequencies, SAW device operation results in objectionable losses and the electrode finger width decreases with increasing frequency of operation. The interdigitated fingers are generally applied by means of a photolithographic fabrication which is limited in the fineness of electrode finger which may be provided.
Accordingly, for operation at elevated microwave frequencies, for example, well into the X-band region to at least 15 to 20 GHz, use is made of magnetostatic wave (MSW) devices which are compact solid state devices including electrodes and a substrate and wherein slow spin magneto-static waves are propagated at microwave frequencies in a low loss ferrimagnetic material placed within a biasing magnetic field. The preferred propagation medium is single crystal yttrium iron garnet (YIG) which is generally grown by liquid phase epitaxy on a matching non-magnetic single crystal substrate of gadolinium gallium garnet (GGG). These MSW devices have lower propagation losses than SAW devices and their photolithographic requirements are minimal owing to their relatively longer wavelengths in the propagating medium.
Single finger transducers in MSW devices result in wideband delay units, however, for many types of signal processing, a relatively narrow band filtering action is desirable. The design of transducers to implement specific device functions currently does not compare with the sophisticated designs of SAW transducers.